1. Field of the Invention
The present invention relates to an organic electroluminescence device and an organic electroluminescence display, and in particular relates to an organic electroluminescence device and organic electroluminescence display in which a plurality of luminescent layers and/or carrier transportation layers are formed between an anode and a cathode.
2. Description of the Related Art
An organic electroluminescence device (, wherein the organic electroluminescence device will be referred to as an “organic EL device” below,) that is easy to miniaturize, has low electrical power consumption, is capable of surface emission, and can use greatly reduced applied voltage compared to a liquid crystal device, and that can be utilized in various kinds of display devices such as a flat display, etc., has attracted attention, and research and development as a next generation luminescent device have been conducted.
FIG. 1 shows a cross-sectional view of a conventional organic EL device. As shown in FIG. 1, the conventional organic EL device 10 has a structure such that an anode 12 made from transparent ITO (Indium Tin Oxide), etc., a hole transportation layer 13, a luminescent layer 14, an electron transportation layer 15, and a cathode 16 are stacked on a transparent glass substrate 11 in order. The hole transportation layer 13 efficiently transports holes to the luminescent layer 14 so as to increase the hole density while the electron transportation layer 15 efficiently transports electrons to the luminescent layer 14 so as to increase the spatial electron density so that the emission efficiency is enhanced. Also, a technology such that a layer for stemming electrons is provided between a luminescent layer and a luminescent layer so as to try to improve the emission efficiency in the luminescent layers has been proposed.
FIG. 2 is a drawing that shows an energy diagram of the organic EL device shown in FIG. 1. As a voltage is applied to the organic EL device 10, the holes 22 move from the anode 12 toward the luminescent layer while the electrons 21 move from the cathode 16 toward the luminescent layer. As the electrons 21 and the holes 22 reach the luminescent layer 14, an organic phosphor contained in the luminescent layer 14 is excited and emits light due to energy released by the recombination of the electrons 21 and the holes 22.
By the way, among the electrons 21 and the holes 22, electrons 21 brought to the anode 12 and holes 22 brought to the cathode 16 without recombining in the luminescent layer 14 are present as shown in FIG. 2 and consumed without contributing to luminescence, so that there is a problem in that the luminance per unit of electric current consumption, that is, the emission efficiency, is lowered.
Additionally, there is also a problem that electrons and holes that have not recombined in the luminescent layer recombine in the hole transportation layer 13 and the electron transportation layer 15, so as to emit luminescence with a color different from a desired color.